System for separating gas

ABSTRACT

An improved system for separating gas from a process stream by providing a stripping unit at the overhead stream of a fractionation column to selectively and effectively remove the gas using a stripping fluid without providing a dedicated light-ends separations unit. The stripper unit may be connected to the reflux drum at the overhead stream. The system for separating gas further achieves greater thermodynamic efficiency by means of a split column design using mechanical vapor recompression with the reboiler and condenser integrated in a falling-film evaporator- or thermosiphon-type vapo-condenser.

FIELD OF THE DISCLOSURE

The disclosure relates to an improved system for separating gases from astream, in particular for removing CO₂ from a methanol synthesis productstream. The system may comprise a stripper portion for removing CO₂ froman overhead stream of a distillation column. The system may furthercomprise a split tower design for the distillation column with anintegrated vapo-condenser and may utilize mechanical vaporrecompression.

BACKGROUND

Global climate change has been deemed to be the “most pressingenvironmental challenge of our time.” The National Aeronautics and SpaceAdministration (NASA) cites that “scientific evidence for warming of theclimate system is unequivocal.” Climate change results from the warmingeffects of greenhouse gases such as water vapor, nitrous oxide, methane,and carbon dioxide. Of these, carbon dioxide emissions are a keyculprit, as global atmospheric concentration of CO₂ has increased by athird since the Industrial Revolution began. CO₂ emissions largely stemfrom human activities, such as the consumption of fossil fuels, thebyproducts of which are emitted into the atmosphere.

One of the ways that nations have attempted to address climate change isby discussing and implementing carbon cap-and-trade policies, which captotal carbon emissions and allow companies to trade for allowances tocreate emissions. Such policies create strong needs for net carbonemitters such as utility and chemical companies to reduce carbonemissions for both the purpose of trading credits to other net carbonemitters and to avoid paying for additional allowances.

In further response to climate change concerns, solar and wind energyproduction has increased significantly in recent years, but stillsuffers from a number of fundamental engineering limitations: most solarand wind energy is primarily available and is therefore produced inareas far removed from population and industrial areas that consume thepower; for example, most wind power potential in the U.S. is in theGreat Plains region, and most solar power potential is in the southwest,whereas population centers are largely concentrated along the coasts.The result of renewable electricity being produced in these remotelocations is high costs and substantial loss of power as the solar andwind power is transmitted over long distances. Additionally, most of theenergy delivered to consumers is not in the form of electricity, butrather in the form of transportation fuel, heating gases, or otherwise.Only a small percentage of transportation energy is provided byrenewable electricity.

Renewable electricity also cannot be stored in industrially significantquantities or at economically feasible costs, which leads to much ofsolar and wind electricity being wasted or grounded during times whensolar and wind production is high but grid capacity is already maxedout, or when demand for electricity is low. As such, solar and windpower are normally underwritten by fossil-fuel sources, such as coal andnatural gas power plants, which may provide baseline or backup powerwhen solar and wind power are not sufficient to meet demand. There istherefore a need for a renewable form of energy that overcomes thedeficiencies of renewable electricity to meet energy demands by storingenergy and facilitating more efficient transportation of the energy tomarkets.

Converting CO₂ into methanol, which is a vital precursor fortransportation fuels, industrial chemicals such as formaldehyde, as wellas plastics, paints, textiles, and other dispositions, is an effectivealternative disposition for CO₂, and an improved method for storingenergy such as from renewable sources as methanol can store therenewable energy in its chemical bonds and overcomes numeroustransportation-related problems of renewable electricity. For instance,the favorable energy density and liquid state of methanol, itscompatibility with transportation fuels, and lower losses duringtransportation render methanol an advantaged energy-storage medium.

Further, given the massive global scale of methanol demand—200,000 tonsper day and growing—diverting CO₂ from the atmosphere and into methanolhas the potential to recycle a large quantity of the greenhouse gasesresponsible for climate change. Methanol also has significant potentialfor growth as a transportation fuel. Another increasing disposition formethanol includes methanol-to-olefins processes that convert methanolinto the building blocks of polyolefins, the most common plastic productfor which there is an ever-growing global demand.

Methanol is typically produced in industrial settings from synthesis gas(“syngas”), a combination of varying amounts of H₂, CO, and CO₂frequently derived from gasified coal. Processes for synthesizingmethanol from syngas typically entrain CO and CO₂ coproducts along withthe methanol product. These coproducts must be separated from themethanol product prior to the final disposition of the product.

Typical processes for removing gases such as CO and CO₂ involve adedicated light-ends separation process, which usually entails separateand capital-intensive fractionation column(s) and associated separationsequipment as well as energy consumption in addition to the primarydistillation column. Energy is consumed in both a reboiler and acondenser for said fractionation operation. The light-ends fractionationprocess is necessary because of the high solubility of CO₂ in methanolwhich cannot therefore be adequately separated by a simple flashoperation. The separation of entrained CO and CO₂ byproducts from thedesired methanol product is, as a result, highly expensive andinefficient.

Reactors used in methanol synthesis from syngas are typically limited toboiling water reactors due to the high heat profile of typical reactionsuites, which include substantial amounts of CO. BWRs are complex andexpensive equipment but are typically necessary in order to mitigate theheat generated from the exothermic production of methanol from syngas inorder to protect the reaction product, the reactor, and the catalyst.

Other processes for separating gases such as CO and CO₂ from a productstream may involve flash separation prior to distillation, but this isnot sufficient or desirable because of its inherently incompleteone-stage equilibrium separation, which sacrifices product to the wastegas stream and does not remove all of the dissolved coproducts.

Other separation processes include membrane separation and solventseparation (such as amine scrubbing), but these processes are costly,inefficient, and ill-suited to methanol production. Consequently,distillation remains the primary method for purifying many chemicalproducts and is one of the most extensively used operations in chemicalprocess industries.

Column distillation or fractionation is a highly energy-intensiveoperation (as distillation uses heat as the separating medium),accounting for 40-60% of the energy used by the chemical processindustry, equivalent to at least 1.2 million barrels of crude oil perday. Distillation alone accounts for 6% of total U.S. energy use and 3%of global energy use. The massive energy consumption of distillationoperations is at least partly due to the inefficiency of existingdistillation processes (5%-10% is normal). An improved separationsprocess therefore has potential to reduce energy-related emissionssignificantly.

From the foregoing, there is a need for an improved system forseparating gases, in particular CO₂, from a product stream, inparticular a methanol product.

SUMMARY

The problem of distillation processes, including in renewabletransportation fuel contexts, being energy- and emissions-intensive, isaddressed by embodiments of the system for separating gas of thedisclosure. An entire distillation stage may be omitted, and associatedenergy expenditure and emissions avoided, by providing an advantagedreaction suite that generates fewer light-end byproducts and aseparations section that removes light-end byproducts such as CO₂ with astripping gas without the need for a dedicated light-ends distillationcolumn.

The separations embodiments described herein are not limited to methanolpurification processes, but may be used in any chemical process whereimproved systems and/or methods for the separation of gases from aprocess stream is required or desired.

An embodiment of the system for separation of gases preferably includesa reactor producing a crude product stream and a fractionation columnconnected at an overhead section to a heat exchanger such as a condenserand a stripper unit. A stripping fluid stream is flowed through thestripper unit to selectively remove impurities such as CO₂ from theoverhead stream of the fractionation column after the overhead streamhas been condensed in the heat exchanger. The reactor may advantageouslyutilize a reaction suite that primarily consumes CO₂ (rather than CO) asa feedstock for methanol synthesis, thereby providing a viablealternative disposition for CO₂ emissions as well as further simplifyingthe separations section, as described below.

The reaction suite may further produce a crude methanol product streamthat comprises substantially only methanol, water, and CO₂. Existingreaction suites produce light end impurities that form azeotropicmixtures with methanol, such as acetone, ethyl formate, methyl acetate,and methyl propionate, with the primarily observed azeotropic impuritybeing acetone. Azeotropic mixtures are extremely difficult to separate,and often require special separations techniques and equipment such aspressure-swing distillation or addition of another chemical species.

Light-end impurities such as these are advantageously avoided by thereaction suite of embodiments of the disclosure, thus effectivepurification of the crude methanol product may be achieved by a singlecolumn-separation followed by a stripping operation, without the needfor a dedicated light ends column to further separate the desiredproduct from impurities in the condensed overhead stream, or a heaviescolumn to remove heavy oil impurities, or other special separationstechniques. This arrangement reduces required fractionation duties,operational complexities, and associated capital costs.

In variations of the system for separating a gas, the stripper unit is agas-sparger unit integrated with a reflux drum, the reflux drum beingconfigured to receive the condensed overhead stream from the heatexchanger. The gas-sparger unit flows or conducts a stripping fluid,such as N₂ or H₂ gas, through the condensed overhead stream in thereflux drum to selectively remove CO₂ from the methanol product withoutthe use of a dedicated separation column to remove CO₂.

The crude methanol composition and stripper unit advantageously allowfor flexible operation, as numerous advantageous stripping fluids may beused, including H₂, N₂ gas, water vapor, natural gas, O₂, noble gases,deuterium, etc. The system may thus be adjusted to the specificconfiguration of products and reactants needed and available in numerousindustrial contexts. For instance, the system may be flexible to allowthe use and production of deuterium to create deuterated methanol, withheavy water byproduct separated during distillation and light-endbyproducts separated from the methanol product through the stripper unitof embodiments of the disclosure.

Existing attempts to utilize stripping technologies to separate gasessuch as CO₂ from methanol product streams are limited by processconfigurations and sources of stripping fluids to pre-distillationstripping. For example, EP 2 831 025 to Akzo Nobel N.V. of Amsterdam,Netherlands discusses the use of H₂ gas to strip certain species out ofa methanol product stream. Noting that wet H₂ sources—H₂ obtained fromaqueous electrolysis processes, particularly production of chlorine orsodium chlorate—are a more affordable source of H₂ than dry H₂ sources(due at least in part to the absence of a dedicated drying step), theembodiments of EP 2 831 025 integrate the drying stages for wet H₂ witha pre-distillation stripping stage. This arrangement necessarily relieson the water that is mixed with the methanol product upstream of thedistillation stage to condense/remove water from the wet H₂ strippingfluid, as the H₂ stripping fluid forms the fresh H₂ feedstock to thereactor. (EP 2 831 025 p. 4 ll. 26-34).

A person skilled in the art would not be motivated nor find it apparentto mount the stripping unit of EP 2 831 025 at the overhead portion of adistillation unit, as EP 2 831 025 is disadvantageously limited to H₂stripping (as H₂ stripping fluid is also the fresh H₂ feed to thereactor, thereby precluding the operational flexibility of usingdifferent stripping fluids at different times, as is contemplated by theembodiments of the disclosure), and is limited to drying a wet-H₂ sourcethrough the water in the pre-distillation product stream. The use of thewet H₂ of EP 2 831 025 to strip the overhead portion of a distillationcolumn would contaminate the overhead product of the distillation withcondensed water, defeating the purpose of the separation entirely andrendering the product methanol less valuable.

In another embodiment of the system for separation of gases, aseparations process for purifying the methanol product makes use of asplit-tower arrangement. The bottom section of the split column mayoperate at a higher pressure than the top section of the split column.The higher operating pressure of the bottom section of the split columnprevents decomposition of the methanol product. The reflux of the bottomsection of the split column may be integrated with the reboiler of thetop section of the split column, utilizing a single heat-exchange deviceto reduce the total duties for the fractionation operation.

In variations of the split-column design, the reboiler of the topsection of the column and the condenser of the bottom section of thesplit column are heat integrated in a single heat-exchange device, forexample a vapo-condenser, owing to the pressure differences between thetop and bottom sections of the split column. Total duty is minimized byutilizing the heat in the higher-pressure column to reboil the bottomsof the lower-pressure column while condensing the overhead stream fromthe higher-pressure column. By heat integrating the columns, therequired duty to be added in the condenser at, the overhead of thelower-pressure column and in the reboiler at the bottom of thehigher-pressure column is reduced. The energy savings realized throughthis arrangement further contributes to emissions reductions.

In particular embodiments, the single heat-exchange device may optimizetemperature approach (and as a result enhance thermodynamic efficiency)between the integrated reboiler and condenser streams and thus betweenthe two columns by utilizing a falling-film evaporator or thermosiphondesign. The improved (lower) temperature approach of falling-filmevaporator- and thermosiphon-type heat exchangers (approximately 1-2. °C.) compared to the temperature approach of kettle reboilers(approximately 10° C.) enables a lower operating pressure in thehigher-pressure column, as the pressure required for the overhead streamto provide sufficient reboiler duty for the lower-pressure column isreduced. This minimizes capital and operating costs (because therequired reboiler duty is reduced and the column itself may be reducedin size) and reduces overall energy consumption, which puts furtherdownward pressure on emissions.

In variations of the split column process, the split column may utilizemechanical vapor recompression to further improve thermodynamicefficiency by taking a side cut from the top section of the column,recompressing the side cut, and then feeding the compressed side cut tothe bottom section of the column.

This advantageously improves the efficiency of the separation bysubstituting the increased temperature and pressure resulting fromrecompressing the side cut for the duty that would otherwise be requiredof a dedicated reboiler for the bottom section of the column. Thisarrangement thereby further reduces capital costs and operating costs.

The overhead condenser may be provided as two condensers in a parallelor series relationship, with a first condenser condensing a firstportion of an overhead stream of a fractionation column, and uncondensedgases from the first condenser being condensed in the second condenser,maximizing the methanol capture without entraining unwanted CO2 gasesback into the liquid methanol product.

Other methods, embodiments, and variations of the system for separatinggases are described in greater detail in the following discussion.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become readily apparent and better understood in view ofthe following description, appended claims, and accompanying drawings.

FIG. 1 is a simplified diagram of a separations system according to thedisclosure.

FIG. 2 is a simplified diagram of an embodiment of the separationssystem of FIG. 1 .

FIG. 3 is a simplified diagram of an alternative embodiment of aseparations system according to the disclosure.

FIG. 4 is a simplified diagram of an alternative embodiment of aseparations system according to the disclosure.

FIG. 5 is a simplified diagram of an alternative embodiment of theseparations system of FIG. 4 .

FIG. 6 is a simplified diagram of an alternative embodiment of a systemfor separating gases according to the disclosure.

FIG. 7 is a plan view of a catalyst support tray according to anembodiment of the separations system.

FIG. 8 is a plan view of a catalyst bed according to an embodiment ofthe separations system.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

A better understanding of different embodiments of the disclosure may behad from the following description read with the accompanying drawingsin which like reference characters refer to like elements.

While the disclosure is susceptible to various modifications andalternative constructions, certain illustrative embodiments are shown inthe drawings and will be described below. It should be understood,however, there is no intention to limit the disclosure to theembodiments disclosed, but on the contrary, the intention is to coverall modifications, alternative constructions, combinations, andequivalents falling within the spirit and scope of the disclosure anddefined by the appended claims.

It will be understood that, unless a term is defined in this patent topossess a described meaning, there is no intent to limit the meaning ofsuch term, either expressly or indirectly, beyond its plain or ordinarymeaning.

The term “stripper unit” as used in this disclosure has its ordinarymeaning and denotes any unit suitable for selectively stripping ordriving a species, preferably a gas, out of another fluid.

The terms “separation column” or “fractionation column” as used in thisdisclosure have their ordinary meaning and denote any columnconfiguration suitable for distilling or separating two or morecomponents, including tray columns, packed columns, binary columns,multi-component columns, split feed columns, or otherwise.

Reaction Suite

Existing methanol synthesis reactions utilize syngas as a feedstock,typically comprising primarily CO, using H₂ to produce methanol usingprimarily the following reaction: CO+2H₂

CH₃OH. However, this reaction yields numerous byproducts that areundesirable in various methanol dispositions and in that they makeseparation of methanol expensive and difficult, both in terms ofrequired equipment and energy costs. There is a need for a reactionsuite that minimizes impurities so as to allow for a simpler and morecost-effective separations process.

FIG. 1 shows a separating system 10 according to an embodiment of thedisclosure. A crude methanol stream 12 is directed from a reactionsection to a fractionation column 14. Crude methanol stream 12 comprisessubstantially only methanol product, water, and CO₂. This composition,which is advantageously free of light end contaminants and heavycontaminants, may be accomplished by synthesizing methanol via acatalyst selection and a reaction suite that uses CO₂ as a startingmaterial rather than CO (such as is used by existing methanolfacilities). In particular, the chemistry is reduced to the followingtwo reactions:

CO₂+3H₂

CH₃OH+H₂O  (Reaction 1)

CO+H₂O

CO₂+H₂  (Reaction 2)

By using Reactions 1 and 2 to synthesize methanol, crude methanol stream12 comprises substantially only methanol, water, and CO₂, simplifyingthe separations process as CO byproduct and undesirable light endcontaminants such as acetone, ethyl formate, methyl acetate, and methylpropionate (with the primarily observed azeotropic impurity beingacetone), are avoided and thus need not be separated. These light endcontaminants are known to create azeotropic mixtures with methanol,separations of which are extremely difficult and costly, as suchmixtures may require using pressure-swing distillation and/or adding athird chemical species to separate.

Heavy contaminants, such as heavy oils, are also largely avoided by theuse of Reactions 1 and 2, simplifying the separation of bottoms productssuch as H₂O. The use of Reactions 1 and 2 further uses CO₂ as a startingmaterial to provide an alternative disposition for CO₂ emissions, andfacilitates a simpler and more efficient separations process, as will bedescribed herein.

In an embodiment, and as will be discussed in greater detail hereafter,Reactions 1 and 2 may take place in a modified reactor. Reactions 1 and2 advantageously have a less intense exotherm than existing reactionsuites for methanol synthesis, enabling the use of tube-cooled reactorsas the primary reactor. The use of a tube-cooled reactor is advantageousover existing reactor configurations, primarily boiling water reactorswhich are required to deal with large exotherms associated with existingreaction pathways, in terms of the lower cost, higher efficiency, andrelative simplicity of operation of tube-cooled reactors. Additionally,tube-cooled reactors are preferred as being more efficient thanadiabatic or cold-shot reactors which are inefficient and requiremultiple reactors in series to achieve desired conversion rates.Further, improving the heat distribution with the reactor helps toprevent catalyst sintering, thereby extending the life of the catalystand minimizes process interruptions.

Utilizing Reactions 1 and 2 further enables the production of methanolto be coupled with GHG-producing processes to recycle CO₂ rather thanemitting CO₂ to atmosphere. For example, the system for separating gasesof the disclosure may be provided at a power plant, oil refinery,chemical plant, mine, manufacturing facility, agricultural facility,heating unit, processing plant, or any other facility, entity, orlocation that emits CO₂. The system may be arranged as a standaloneunit, an integrated unit, or as a bolt-on unit.

Gas Stripper

Because all distillation processes require energy input, often throughthe reboiler and condenser, to achieve separation of the components, andtherefore produce emissions, there is a need for a separations sectionthat minimizes the number of distillation operations required to achievedesired separation of the components, and consequently minimizesequipment and operating costs, as well as emissions. Existing methanolsynthesis operations typically comprise a column that is dedicated toseparating light components (meaning components having a lower boilingpoint than the methanol product such as CO, CO₂, etc.), and consequentlygenerate emissions. There is a need for a process that eliminates theneed for a dedicated column with its associated emissions to separatecomponents.

In an embodiment of the disclosure depicted in FIG. 1 , reactor effluentcontained in crude methanol stream 12 is fed to separations section 10which comprises fractionation column 14 and accompanying equipment.Owing to the composition of the crude methanol stream 12 which containsmethanol, water, and virtually no CO or other light contaminants besidesCO₂, only a single fractionation column 14 is required for purifying thedesired methanol product. This is a singular advantage over mostmethanol purification processes which comprise dedicated light endscolumns and associated equipment such as reboilers, condensers, drums,etc. in order to achieve adequate purification of the product. Acondenser 16 and a reboiler 32 provide the required duty for thefractionation column 14 to separate the crude methanol stream 12 intoon-spec products. The fractionation column 14 may comprise a strippingsection, a rectifying section, and a feed section.

An overhead stream 15 of the fractionation column 14 comprises bothmethanol and CO₂, as the water is less volatile and therefore iscollected and sent to battery limits or other processes via a bottomstream 33. The overhead stream 15 is condensed in a condenser 16 andthen stripped of CO₂ in an integrated stripper/reflux drum 18.Integrated stripper/reflux drum 18 comprises a stripper portion 22 whichis connected to a reflux drum 20. The integrated stripper/reflux drum 18advantageously removes dissolved CO₂ from the methanol product withoutthe use of heat or a separate, dedicated fractionation column, reducingenergy requirements and therefore emissions.

The integrated stripper/reflux drum 18 drives the CO₂ out of themethanol in the condensed overhead stream by introduction of a strippingor carrier gas such as H₂, N₂, or other suitable gas. Other suitable gasspecies may include natural gas, noble gases, O₂, water vapor,deuterium, etc., depending on process requirements and facilityconsiderations. For example, N₂ may be abundantly available in certainchemical plants with which the system for separating gases is associatedand may recommend itself as a suitable stripping gas. In certainpetrochemical or refining facilities, H₂ may be more abundantlyavailable and therefore may be suitable as a stripping gas. Otherfacilities, infrastructure constraints, and economic considerations mayrecommend other gaseous species as stripping gases.

In an embodiment of the system, the stripper portion 22 is a gas spargerwhich is integrated with the reflux drum 20. The gas sparger 22introduces the carrier gas from the stream 24 into the condensedoverhead stream 15 collected within the reflux drum 20, the carrier gascontacting and entraining the dissolved CO₂, thereby stripping the CO₂out of liquid methanol in the reflux drum 20. The gas sparger 22 may, inan embodiment, introduce the carrier gas by bubbling the carrier gas upthrough the collected liquid within the reflux drum portion 20 of theintegrated stripper/reflux drum 18. The combined carrier gas and CO₂ areejected from the integrated stripper/reflux drum 18 in the form of awaste gas stream 26 that may be disposed of in various ways; forexample, the waste gas stream 26 may be scrubbed of entrained methanolin a scrubber unit prior to being released to the atmosphere or beingrecycled/reprocessed as additional feedstock to the reactor.Alternatively, the waste gas stream 26 may be fed directly back into theloop as additional feedstock or disposed directly to battery limits oranother process.

The remaining liquid methanol in the reflux drum 20 is split between areflux stream 28 which is directed back to the fractionation column 14to facilitate the distillation of methanol and CO₂ from water and otherheavy components, and a methanol product 30 which may be directed tobattery limits, storage, or other disposition. Thus by utilizingReactions 1 and 2 to produce a crude methanol stream comprisingsubstantially only methanol, CO₂, and water, and by driving off thedissolved CO₂ from the overhead stream 15 of a single fractionationcolumn 14 without the use of added heat by introducing a carrier gas ina stripper unit 22, on-spec methanol product 30 may be obtained withoutthe use of a dedicated light-ends column, with its attending capital andenergy expenditures.

In an alternative embodiment depicted in FIG. 2 , a crude methanolstream 52 which similarly comprises substantially only methanol, water,and CO₂ is fed to a separations section 50 which comprises a singlefractionation column 54. A condenser 56 and a reboiler 73 providerequired duty for the fractionation column 54 to separate crude methanolstream 52 into on-spec products, including a methanol product 66 and awaste water product 74. The overhead stream from the fractionationcolumn 54 is condensed in the condenser 56 and fed to a stripper unit60. Unlike the embodiment of FIG. 1 , the stripper unit 60 is notintegrated or integrally formed with the reflux drum 62. A carrier gasis fed to the stripper unit 60 via stream 71, and waste gas stream 72comprises combined carrier gas and CO₂ which has been removed from themethanol product in the stripper unit 60. As with the waste gas stream26 of FIG. 1 , the waste gas stream 72 may be disposed of such as bybeing scrubbed of entrained methanol prior to atmospheric release or maybe recycled/reprocessed as additional feedstock to the reactor.

Stripped liquid methanol is fed from the stripper unit 60 to the refluxdrum 62, and is then split into a methanol product stream 66 which maybe disposed toward battery limits, storage, or other processes, and areflux stream 65, which is returned to the fractionation column 54 asreflux to facilitate the distillation of methanol and CO₂ from water andany other heavy contaminants.

The embodiment depicted in FIG. 2 demonstrates that the stripper unit 60need not be integrally formed with the reflux drum 62 but rather may beseparately arranged, as determined by the process requirements of aspecific configuration or facility. For example, in a retrofitoperation, a stripper unit may be provided to cooperate with an existingdrum of an existing distillation column, or vice versa.

In an alternative embodiment depicted in FIG. 3 , a crude methanolstream 76, which comprises substantially only methanol, water, and CO₂,is fed to a separations section 75 which comprises a singlefractionation column 77 and associated equipment. A condenser 78 and areboiler 87 provide the required duty for the fractionation column 77 toseparate crude methanol stream 76 into on-spec products, including amethanol product 86 and a waste water product 89. An overhead streamfrom the fractionation column 77 is condensed in the condenser 78.

In the embodiment of FIG. 3 , the condensed overhead stream is splitinto two streams. A stream 80 contains a first fraction of CO₂ as wellas entrained methanol and may be removed from the process as itcomprises mainly gas, thanks to a condenser 78 facilitating a roughseparation of gaseous CO₂ (containing entrained methanol) and liquidmethanol (containing dissolved CO₂). As with waste gas streams 26 and 72in the aforementioned embodiments depicted in FIGS. 1 and 2 , the stream80 may be scrubbed of entrained methanol prior to atmospheric release ormay be recycled/reprocessed as additional feedstock to the reactor. Thescrubbed methanol may be returned to the process as reflux, added to themethanol product stream, or otherwise disposed to another process or tobattery limits.

A remaining portion of the condensed overhead stream containingprimarily liquid methanol with dissolved CO₂ is sent to a reflux drum79. After being collected in the reflux drum 79, the remaining portionof the condensed overhead stream may be split, with a portion or astream 81 returning to the fractionation column 77 as reflux tofacilitate the distillation, and a portion or stream 82 being sent tothe stripper unit 83 for removal of dissolved CO₂. As with the stripperunits 22 and 60 of the aforementioned embodiments, the stripper unit 83drives dissolved CO₂ out of the liquid methanol through the introductionof a carrier gas such as H₂, N₂, or any other suitable species in astream 84, as discussed previously.

The stripper unit 83 produces a waste gas stream 85 comprising thecarrier gas, CO₂, and some amounts of entrained methanol. The waste gasstream 85 may be scrubbed of entrained methanol product prior toatmospheric release and/or recycled/reprocessed as additional feedstockto the reactor. Because the first fraction of CO₂ was removed from theprocess via stream 80, waste gas stream 85 contains less CO₂ than stream80 and waste gas streams 26 and 72 of the aforementioned embodiments onboth a mass flow basis and a mass fraction basis. As such, waste gasstream 85 may be suitable for different dispositions than waste gasstreams 26 and 72 due to its lower CO₂ content. On-spec methanol productin stream 86 is obtained in this embodiment from a bottom portion ofstripper unit 83.

The embodiment depicted in FIG. 3 demonstrates that the stripper unit 83may be arranged either upstream or downstream of a reflux drum 79, asdetermined by the process requirements of a specific configuration orfacility, and that certain gases may advantageously be separatedupstream of a reflux drum, rendering the stripped gas viable fordifferent dispositions.

A reboiler 87 provides duty necessary to reboil a bottom fraction of thecrude methanol stream 76, vaporizing methanol product and CO₂ whilecollecting water and any other trace heavy species, such as long-chainalkanes, higher alcohols, higher ketones, and esters of lower alcoholswith formic, acetic, and propionic acids. The fractionation column 77removes a waste water stream 89 from a bottom portion.

By providing the aforementioned embodiments, the problem of separationsprocesses, in particular crude methanol purification, requiring adedicated light-ends fractionation column with its associated emissionsto remove gaseous species, such as CO₂, is advantageously solved.

Split Tower Arrangement

Distillation is a highly energy-intensive process because of theinherent inefficiency of the separation process, which requires largeduties in both the reboiler and condenser, as well as significant refluxrates to achieve desired separation. This leads to high operating andcapital costs. In facilities or processes where substantial heat is leftover from initial reaction units (due to reaction or thermalinefficiencies, or high reaction exotherms) or from associated processesat the same facility or site as the separation process, the leftoverheat often being in the form of generated steam, waste heat may be usedto provide duty to the reboiler of certain distillation operations.

However, such an arrangement may be undesirable in the first instance,as the generation of substantial waste heat in the reaction phase or inassociated processes represents a thermodynamic inefficiency andconsequently a negative effect on emissions from the facility. It istherefore desirable to minimize the generation of waste heat as much aspossible as opposed to trying to salvage the waste heat. Accordingly, itis also desirable to minimize heat requirements of processes locateddownstream of the reaction process which may otherwise utilize wasteheat, such as in reboilers. By so doing, requirements for added heat maybe reduced. There is a need for an improved separations process whichenhances thermodynamic efficiency in order to minimize heat requirementsand consequently energy expenditures and emissions.

In an alternative embodiment of a system for separating gases depictedin FIG. 4 , a crude methanol stream 102 is fed to a separations section100, which comprises a fractionation column 104. The fractionationcolumn 104 is arranged in a split-tower arrangement comprising a top orlow-pressure (LP) section 106 and a bottom or medium-pressure (MP)section 108. The LP section 106 and the MP section 108 are connected bystream 140 which comprises primarily methanol and water, as well as byheat integration between the condenser of the MP section 108 and thereboiler of the LP section 106. A vapo-condenser 110 integrates thefunctions of both condensing an overhead stream 144 of the MP section108 and reboiling a bottom stream 142 of the LP section 106. Theoperating pressure of the MP section 108 is calibrated to besufficiently high such that the condensation of a stream 144 providesthe required duty to reboil a stream 142.

The use of the split-tower arrangement of the separations section 100enhances thermodynamic efficiency by reducing the total duty required inthe fractionation column 104, as the duties that are integrated in thevapo-condenser 110 would otherwise be provided in a condenser at theoverhead of the MP section 108 and a reboiler at the bottom of the LPsection 106, or in increased duties to the LP section 106 condenser andthe MP section 108 reboiler.

As in certain previous embodiments, an overhead stream comprisingsubstantially only CO₂ and methanol from LP section 106 is fed to acondenser 112 and then to an integrated stripper/reflux drum 114 whichcomprises a stripper section 116 and a reflux drum 118. The strippersection 116 and reflux drum 118 may, in alternative embodiments, bedistinct units, such as is shown in the embodiment depicted in FIG. 2 ,as required by process configurations and/or facility requirements. CO₂is removed from the condensed methanol by introduction of a carrier gas,provided through a stream 126. In certain embodiments, the strippersection 116 is a gas sparger. The gas sparger 116 introduces the carriergas from the stream 126 into the condensed overhead stream in refluxdrum 118 to drive the dissolved CO₂ out of solution with the liquidmethanol and into a waste gas stream 128, which comprises substantiallyonly CO₂ and carrier gas. The carrier gas may be N₂, H₂, or any othersuitable and/or inert gas, such as water vapor, natural gas, noblegases, O₂, deuterium, etc., as required by specific process needs andproduct requirements. As with previous embodiments, the waste gas stream128 may be scrubbed of entrained methanol prior to atmospheric releaseor being recycled/reprocessed as additional feedstock to the reactor.

The liquid methanol from reflux drum 118 is split into a reflux stream132 which is returned to the LP section 106 to facilitate thedistillation of methanol and CO₂ from water, and the LP section methanolproduct stream 134 which may be disposed similar to previousembodiments.

The MP section 108 separates the contents of a stream 140 into productmethanol and waste water. Substantially no CO₂ is entrained in stream140 because the CO₂ contained in the crude methanol stream 102 isisolated in the overhead stream of the LP section 106. A reboiler 122provides duty at a bottom portion of the MP section 108. A waste waterproduct is obtained at the bottom of the MP section 108 and is disposedof via a stream 124. A reflux drum 120 receives the condensed overheadstream of the MP section 108 and splits the condensed overhead streaminto a reflux stream 138 which is returned to the MP section 108, and aMP section methanol product stream 136 which is combined with the LPsection methanol product stream 134. A combined methanol product stream130 can be sent to battery limits, storage, or to another disposition.In this embodiment, the MP section 108 does not comprise a stripper unitbecause substantially no CO₂ is entrained in the stream 140 and on-specmethanol product is obtained in the stream 136 without a dedicated unitto remove CO₂.

In alternative embodiments of the disclosure, a second stripper unit maybe connected to the MP section reflux drum 120 in the same manner as astripper section 116 is attached at the LP section reflux drum 118. Asplit stream from a stream 126 or a separate stream introduces carriergas to the second stripper unit connected to the MP section reflux drum120, and a waste stream comprising carrier gas and any CO₂ that isremoved from the condensed overhead stream from the MP section 108 joinswith a waste gas stream 128 to battery limits, scrubbing, or recycle.This embodiment may be employed, for example, to ensure that any traceCO₂ that is potentially entrained into MP section 108 is eliminated fromthe MP section methanol product. This may be desired in configurationsproducing methanol of exceptionally high purity.

In particular, this embodiment may be advantageous if, for example, thestream 140 comprises a sidecut stream rather than a bottom stream, or ifthe crude methanol stream 102 is fed to the MP section 108 rather thanto the LP section 106. The second stripper unit may be integrallyconnected to the reflux drum 120, or may be separate, as in theembodiment depicted in FIG. 2 . Additionally, in certain embodiments itmay be advantageous to feed the crude methanol stream 102 to thefractionation column 104 at a location at the MP section 108, in whichcase a second stripper unit on the MP section 108 is desirable.

In yet further embodiments of the disclosure, the stripper section 116may be distinct from the LP section reflux drum 118, as in theembodiment depicted in FIG. 2 .

By providing the features of the depicted embodiment, the problem ofseparations processes requiring large amounts of energy and consequentlygenerating unnecessary emissions, is advantageously addressed as thesplit-tower arrangement reduces required duties by integrating thereboiler and condenser of the LP section 106 and MP section 108,respectively in a single device.

Mechanical Vapor Recompression or Heat-Pump Distillation

In certain applications, available heat and/or steam (which is normallyused to provide reboiler duty) is limited; for example, certainprocesses may not have a high exotherm and thus do not producesignificant amounts of waste heat for steam generation which can be usedto provide heat to other processes. In such applications, and indistillation generally, a separations section which minimizes heatrequirements, such as in reboilers, is desirable to avoid the costs,both capital and operational, associated with steam generation to makeup for heat recovered from hot sections of the process. Additionally, itis desirable to minimize capital costs by reducing the size and numberof units required to carry out a separation operation.

In another embodiment of the disclosure depicted in FIG. 5 , aseparations section 200 utilizes mechanical vapor recompression tofurther enhance the thermodynamic efficiency of the separation process.A crude methanol stream 202 containing substantially only methanol,water, and CO₂ is fed to a fractionation column 204, which is arrangedin a split-tower arrangement similar to the embodiment of FIG. 4 . A topor LP section 206 is heat integrated with a bottom or MP section 208 ata vapo-condenser 210 which condenses an overhead stream of the MPsection 208 and reboils a bottom stream of the LP section 206, enhancingoverall efficiency. A crude methanol stream 202 is received at anoptimal location in the MP section 208. In alternative embodiments, thecrude methanol stream 202 may be received at an optimal location in theLP section 206.

The LP section 206 and the MP section 208 are further connected bystreams 240 and 242, which function to provide material balance andespecially, in the case of a stream 242, to provide reflux for the LPsection 206, thereby eliminating the need for a separate reflux streamfrom an overhead stream of the LP section 206. A waste water product isremoved from the bottom of the LP section 206 in a stream 244.

As with previous embodiments, a condenser 212 condenses an overheadstream of the LP section 206 and feeds the condensed overhead stream toan integrated stripper/reflux drum 214. An integrated stripper/refluxdrum 214 comprises a stripper unit 216 and a drum 218, the stripper unit216 configured to selectively remove CO₂ from the methanol product byintroducing a carrier gas from stream 226. As in previous embodiments,the stripper unit 216 and drum 218 may alternatively be distinct units(as shown in the embodiment of FIG. 2 ), and stripper unit 216 may bedownstream of the drum 218, as in the embodiment of FIG. 3 . In yetfurther embodiments, the stripper unit 216 may be a gas sparger, as inthe embodiment depicted in FIG. 1 .

CO₂ and carrier gas from the integrated stripper/reflux drum 214 aredisposed of in waste gas stream 228, which may be scrubbed of entrainedmethanol prior to atmospheric release and/or recycled/reprocessed asadditional feedstock for the reactor. The remaining liquid in the refluxdrum 218 is fed via a stream 220 to be combined with methanol productfrom the MP section 208 to deliver an on-spec methanol product 232.Because the stream 242 provides reflux from the MP section 208, noreflux stream needs to be returned to the LP section 206 from the LPsection 206 overhead stream. As a result, the required flowrate of theLP section 206 overhead stream is reduced and the required size of acondenser 212, as well as duty removed therethrough via cooling water,is consequently reduced. This advantageously reduces capital andoperating costs, as well as emissions. In certain such embodiments, thedrum 218 may be omitted.

An overhead stream from the MP section 208 is condensed in avapo-condenser 210 and collected in a drum 222. From the drum 222, areflux stream 234 may be directed to the MP section 208, and a methanolproduct stream 230 may be joined to the methanol product stream 220.

A sidecut from the LP section 206 is fed to a mechanical vaporrecompression compressor (MVR compressor) 236 which compresses thesidecut to an operating pressure suitable for the MP section 208,thereby also raising the temperature of the sidecut. The recompressedsidecut 238 is fed to the MP section 208, preferably at a location nearthe bottom of the MP section 208. In this embodiment, the recompressedsidecut 238 replaces in its entirety the reboiler of the MP section 208,as the added enthalpy of the compressed sidecut serves to provide thenecessary duty to reboil the MP section 208 and consequently the LPsection 206. The addition of this duty by the MVR compressor 236achieves enhanced thermodynamic efficiency and capital cost reductionscompared to providing the duty through a reboiler unit.

Recompression of a stream may thus advantageously utilize compressorwork to raise the pressure and consequently temperature of a portion ofa process stream (such as a sidecut from a column 206) for the purposesof providing reboiler duty more efficiently than adding heat to theprocess through a conventional reboiler, especially a reboiler utilizingsteam as a heat source and with fewer emissions. Recompressing anexisting vapor stream to a higher temperature and pressure using acompressor advantageously bypasses the phase change inefficienciesinherent in steam generation from boiler feed water due to the highenthalpy difference between boiler feed water and pressurized steam.Mechanical vapor recompression therefore attains the desired increase intemperature and pressure with a much lower input of energy thantraditional reboilers.

The efficiency of the mechanical vapor recompression is further enhancedby feeding the recompressed sidecut 238 directly to a bottom portion ofthe MP section 208 to replace the reboiler and the heat exchangeinefficiencies associated therewith. The recompressed sidecut 238 canmore efficiently transfer heat to the MP section 208 by interactingdirectly with the contents of the fractionation column 204. Thisarrangement reduces heating duties and capital costs by replacing thereboiler and its associated energy inputs with a recompressed processstream that adds heat directly to the contents of the MP section 208.

The use of mechanical vapor recompression thus addresses the problem ofdistillation and other process operations requiring added heat, whichleads to increased emissions, by reducing heat requirements and capitalcosts through the use of mechanical vapor recompression of, for example,a sidecut stream.

In an alternative embodiment according to the disclosure depicted inFIG. 6 , a dual-condenser arrangement may be provided at an overhead ofa fractionation column. Crude methanol product may be separated fromwater and other heavy byproducts (if any) in the fractionation column(not shown), with an overhead stream 302 being conducted from thefractionation column to first and second condensers 312A, 312B. Theoverhead stream 302 may first be condensed to a first temperature in thefirst condenser 312A, with a portion of the overhead stream 302 beingcooled in the first condenser 312A to a liquid state and a portion ofthe overhead stream 302 remaining in a gaseous state. The firstcondenser 312A may provide heat transfer through the medium of coolingwater, refrigerant, or any other suitable medium introduced at a stream311A and removed at a stream 313A.

The portion of the overhead stream 302 that remains in a gaseous stateafter being cooled in the first condenser 312A is conducted at a stream304 to the reclaimer or second condenser 312B, where it may becooled/condensed against a second medium introduced at a line 311B andremoved at a line 313B. As with the first condenser 312A, the secondcondensing/cooling medium may comprise cooling water, refrigerant, orany other suitable medium provided in flow rates, temperatures, andpressures configured to effect a desired amount of condensation in thesecond condenser 312B.

The portion of the overhead stream 302 that was condensed to a liquidstate in the first condenser 312A may be conducted at a stream 306towards a stripping column 316. Similarly, the portion of the overheadstream 302 that was condensed to a liquid state in the second condenser312B may be conducted at a stream 308 to the stripping column 316. Thestreams 306, 308 may be added to the stripping column 316 at a sameheight or different heights, or may be mixed together prior to beingadded to the stripping column 316. Owing to the amount of the overheadstream 302 that is condensed in the first condenser 312A, the secondcondenser 312B may be of reduced size relative to the first condenser312A, providing capital expense reduction.

The embodiment of FIG. 6 may be arranged to operate in single-condensermode or in dual-condenser mode. A valve 307 may be arranged on thestream 304 such that if the valve is closed, the system may operate insingle-condenser mode wherein the gaseous portion of the overhead stream302 exiting the first condenser 312A and the stripping gas exiting thestripping column 316 at stream 305 is vented via a stream 309, and maybe disposed to recycle, atmosphere, or otherwise.

If the valve 307 is open, the system may operate in dual-condenser modewherein the gaseous portion of the overhead stream 302 exiting the firstcondenser 314 at stream 304 and the stripping gas exiting the strippingcolumn 316 at stream 305 is conducted to the second condenser 312B to befurther condensed. A vent line 310 is provided to dispose gasesremaining after overhead stream 302 and the stripping gas have beenfurther condensed in the second condenser 312B to recycle, atmosphere,or otherwise.

The stripping column 316 may be formed as a packed column, with randompackings 350 facilitating a greater surface area over which the liquidportions of the overhead stream 302 may be contacted with a strippinggas, such as H₂, N₂, or any other suitable stripping gas as discussed inprevious embodiments. The stripping gas may be introduced via a line314, which may be configured to enter the stripping column 316 near abottom portion thereof, allowing the stripping gas to rise through therandom packings 350 as the liquid portions of the overhead stream 302fall downward through the stripping column 316, with the stripping gasprovided in quantities, temperatures, and pressures suitable foreffecting a desired separation of CO₂ entrained in the liquid portionsof the overhead stream 302. In alternative embodiments, the strippingcolumn 316 may be arranged as a trayed column or any other suitableconfiguration of separation unit, and with the stripping gas being fedto the stripping column 316 at any suitable location.

The stripping gas and stripped CO₂ and other gases may exit thestripping column 316 via a line 305, thereafter to join the line 304.Any entrained gases, including methanol, contained in the stripping gasexiting the stripping column 316 may be fed to the second condenser 312Bto condense any entrained methanol product out of the stripping gaswithout condensing so much gas as to cause an undesirable degree of CO₂entrainment in the liquid portion in the line 308.

Accordingly, the temperatures at which the first and second condensers312A, 312B operate may be selected to optimize an amount of methanolcondensed in the first and second condensers 312A, 312B without reducingthe temperature of the overhead stream 302 and components thereof to adegree that entrains an undesired degree of CO₂ in the liquid productsproduced in the condensers 312A, 312B. Fluids that are not condensed toliquid and returned to the stripping column 316 are vented, recycled, orotherwise disposed via a line 310.

The liquid portion of overhead stream 302, now stripped of CO₂, may flowto a reflux drum 318, with a pump 320 operating to conduct the liquidportion of the overhead stream 302 either via a line 332 to thefractionation column as reflux, or via a valve 322 and a line 334 to amethanol product disposition. The amount of reflux may be determinedbased on the fractionation column, particularly based on a requiredreflux ratio.

In an alternative arrangement, the stripping gas may be provided at thereflux drum 318, with the stripping gas and stripped CO₂ arranged toflow upwards through a line connecting the reflux drum to the strippercolumn, with the liquid portion of the overhead product 302 flowingdownward through the same line, with may be arranged for self-drainingflow. The depicted embodiment is not limited, but rather the equipment,streams, and other components may be altered within the spirit and scopeof the disclosure.

By providing a separations section comprising a fractionation columnarranged with a stripping unit at the overhead product or stream, theprocess of purifying a methanol product stream is simplified andrealizes capital and operational cost savings, as a dedicated light-endsfractionation column and associated equipment may be omitted. Thestripping unit is able to effectively remove CO₂ and other componentswithout the use of added heat and fractionation systems while realizingor in combination with thermodynamic enhancements.

Deuterated Methanol Production and Deuterium Recovery

In an alternative embodiment of the disclosure, the system forseparating gas may be arranged to separate the byproducts of adeuterated methanol formation process. Deuterated methanol is gainingincreasing attention as a precursor for intermediates in the preparationof deuterated drugs and is also a valuable solvent often used in nuclearmagnetic resonance (NMR) spectroscopy, among other dispositions.Deuterium may be provided to a reactor as an alternative feedstock tohydrogen in the previously described Reactions 1 and 2, with a resultingformation from CO₂ and deuterium of deuterated methanol, deuterated(“heavy”) water, unreacted feedstock, and other light-end byproducts.The system for separating gas may be modified to enable recovery andrecycle of unreacted deuterium from the crude deuterated methanol in thereactor effluent, in particular by using a stripping tower at theoverhead of a column according to the disclosure.

Heavy water recovered at the bottom of a fractionation column accordingto the disclosure may be processed in an electrolyzer to separate theheavy water into oxygen and deuterium. The deuterium may then berecycled as reactor feedstock, with mass controllers ensuring a properratio of reactants fed to the reactor. The fractionation column overheadproducts, including deuterated methanol, may be separated according toembodiments of the disclosure using a stripping column arranged at theoverhead of the fractionation column to drive off CO₂ and otherlight-end byproducts and contaminants without the need for a dedicatedlight-ends column as described herein. The stripping gas may be N₂, O₂,steam, deuterium, or any other suitable gas.

The stripping gas and unreacted feedstock recovered from the crudemethanol product therewith may be advantageously recycled as feedstockto the reactor, with the aforementioned mass controllers ensuring aproper ratio of reactants fed to the reactor.

Selection of Vapo-Condenser Heat Exchanger

The thermodynamic efficiency of the separation process is largelydependent on the efficiency of the exchange of heat in thevapo-condenser as depicted in the split tower embodiments of FIGS. 4 and5 , as the heat transfer efficiency is inversely related to the pressurerequired in the MP section of the separation column in order to providesufficient reboiler duty for the LP section. The better the efficiencyof heat transfer in the vapo-condenser, the lower the required pressurefor the MP section so as to be sufficient to provide the reboiler dutyfor the LP section. Lower pressure in the MP section translates tobetter thermodynamic efficiency of separation (lower reboiler duty ormechanical vapor recompression work) and a lower capital cost (as thewalls of the column may be less thick). As such there is a need for aheat exchange in vapo-condenser that maximizes the efficiency in orderto minimize the operating pressure of the MP section.

Kettle-type reboilers, which are typical in existing processes, andwhich allow the transfer of large duties in a relatively compact design,typically have an approach temperature between the heating and coolingmedia of about 10° C. An approach temperature this large unfortunatelyleads to inefficient heat transfer and therefore lower efficiency andhigher capital costs, as the pressure in the MP section needs to behigher in order to provide reboiler duty to the LP section. This resultsin a more expensive column (because thicker walls are required tocontain the higher pressure) and increased reboiler duty required in theMP section to maintain the higher pressure and temperatures. Energyexpenditures and as a result emissions are correspondingly increased.

In certain embodiments of the disclosure, the vapo-condenser of thesplit tower embodiments depicted in FIGS. 4 and 5 (110, 210,respectively) is not a kettle-type reboiler but is rather either athermosiphon-type heat exchanger or a falling film evaporator-type heatexchanger. Thermosiphon-type heat exchangers or falling filmevaporator-type heat exchangers serve to improve the thermodynamicefficiency in that the approach temperature in both (˜1°) is lower thanthe approach temperature (˜10°) in kettle-type reboilers. By decreasingthe approach temperature, the required operating pressure of the MPsection is reduced because the MP section need not reach the higher Trequired by an otherwise higher temperature approach. The resultinglower pressure of the MP section also reduces energy expenditures andemissions.

The use of thermosiphon-type or falling film evaporator-type heatexchangers thus advantageously addresses the problem of vapo-condensersnot offering sufficiently close approach temperatures and optimizes theMP section operating conditions for greatest thermodynamic efficiency.

Reactor Design

Reactor design in methanol synthesis and in any chemical process isimportant for preserving catalyst life, for achieving acceptable productrate and quality, and for controlling process conditions. Existingmethanol synthesis facilities typically comprise boiling water reactorswhich are expensive and complex but are required in order to handlelarge temperature peaks due to the exothermic nature of methanolsynthesis.

Alternative reactors in existing methanol synthesis facilities typicallycomprise adiabatic or cold-shot reactors, which are less expensive thanboiling water reactors but are inefficient and require the use ofmultiple reactors in order to achieve acceptable conversion rates.Existing facilities typically require a plurality of reactors, whetherthe reactors or boiling water reactors, adiabatic reactors, or acombination of boiling water reactor and adiabatic reactor.

Existing reactor designs, because of the high temperatures normallypresent in methanol synthesis and other exothermic processes furtherexperience problems with catalyst sintering, wherein the normallycrystalline catalyst reverts to its agglomerate state due to the highheat. Sintering reduces the effective life of the catalyst, leading toincreased costs as the facility and process must be interrupted to allowfor the catalyst to be removed, regenerated, and replaced, oralternatively increases costs as redundant reactor systems must beinstalled to allow for catalyst swap out without shutting down thefacility.

Existing reactor designs often comprise a hollow section in the centerof the reactor which is used to structurally support the weight of thecatalyst, e.g. by providing additional mechanical structures orsupports. This unfortunately has the effect of unevenly distributing thecatalyst, reactants, and cooling tubes (in tube cooled reactors).

Accordingly, there is a need for a reactor (and reaction suite) thatallows for the use of a single tube-cooled reactor to minimize capitalcosts, technical complexity (and thus maintenance costs and down-time),and operating expenses.

The above problems are addressed by the selection of Reactions 1 and 2to synthesize methanol, which results in a lower heat profile thanexisting methanol synthesis reaction suites. As a result of the lowerheat profile, a boiling water reactor is not required in order tocontrol the temperature of the reactor. A tube-cooled reactor istherefore sufficient to control the temperature resulting from theReactions 1 and 2. Moreover, a single tube-cooled reactor is sufficientto produce the desired methanol product as it is more efficient thanadiabatic reactors due to its lower operating temperature, and multiplereactors in series are not required for sufficient conversion. Thus byselecting Reactions 1 and 2, a single tube-cooled reactor mayadvantageously be used to achieve desired methanol production.

In an embodiment of the disclosure depicted in FIG. 7 , a cross-sectionof a reactor 400 for converting CO₂ into methanol is shown. In animproved design of a tube-cooled reactor, new tubes 410 are added to thecatalyst support plate 420. The addition of the tubes 410 help todistribute heat more effectively and consistently in the reactor 400.The more even heat distribution prevents hot spots and thus minimizescatalyst sintering, thereby extending the useful life of the catalystbetween regenerations.

In another embodiment of the disclosure depicted in FIG. 8 , an improvedcatalyst bed 500 is provided, with tubes 510 running through thecatalyst bed in an even distribution to create an even heatdistribution. Perforations 520 additionally provide for even catalystmixing.

It is to be understood that not necessarily all objects or advantagesmay be achieved under any embodiment of the disclosure. Those skilled inthe art will recognize that the system for separating gas including CO₂may be embodied or carried out in a manner that achieves or optimizesone advantage or group of advantages as taught without achieving otherobjects or advantages as taught or suggested.

The skilled artisan will recognize the interchangeability of variousdisclosed features. Besides the variations described, other knownequivalents for each feature can be mixed and matched by one of ordinaryskill in this art to make or use a system for removing light gases underprinciples of the present disclosure. It will be understood by theskilled artisan that the features described may be adapted to othertypes of chemical species and processes. Hence this disclosure and theembodiments and variations thereof are not limited to methanol synthesisprocesses or to removing CO₂, but rather can be utilized in any chemicalprocess wherein removing a gas species is desired or required.

Although this disclosure describes certain exemplary embodiments andexamples of system for removing gas, it therefore will be understood bythose skilled in the art that the present disclosure extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the disclosure and obvious modifications and equivalentsthereof. It is intended that the present disclosure should not belimited by the particular disclosed embodiments described above.

1. A system for separating a gas from a process stream, the systemcomprising: a separation unit configured to receive the process streamof a chemical process and to separate at least one component of theprocess stream, the separation unit comprising a first heat exchangerlocated at an overhead portion of the separation unit and receiving anoverhead stream of the process stream from the overhead portion of theseparation unit, the first heat exchanger being configured forcondensing at least a portion of the overhead stream of the processstream; a stripper unit configured to receive the condensed portion ofthe overhead stream of the process stream from the first heat exchanger,the stripper unit being configured for separating the gas from thecondensed portion of the overhead stream of the process stream byintroducing at least one stripping fluid thereunto; and wherein theseparation unit is a split column comprising a relatively high-pressurecolumn and a relatively low-pressure column, the system furthercomprising a second heat exchanger, wherein the first heat exchanger islocated at an overhead portion of the relatively low-pressure column,and the second heat exchanger is located at an overhead portion of therelative high-pressure column.
 2. The system for separating a gas from aprocess stream of claim 1, wherein the process stream comprises CO₂,water, and methanol.
 3. The system for separating a gas from a processstream of claim 1, wherein the chemical process is a methanol synthesisprocess.
 4. The system for separating a gas from a process stream ofclaim 3, wherein the chemical process is a methanol synthesis processthat synthesizes methanol from CO₂ and H₂.
 5. The system for separatinga gas from a process stream of claim 1, wherein the at least onestripping fluid comprises at least one of gaseous N₂ or H₂.
 6. Thesystem for separating a gas from a process stream of claim 1, wherein atleast one waste gas stream comprising a portion of the at least onestripping fluid and a portion of the separated gas is generated.
 7. Thesystem for separating a gas from a process stream of claim 6, whereinthe at least one waste gas stream is generated from the stripper unitand is recycled upstream.
 8. The system for separating a gas from aprocess stream of claim 6, wherein the at least one waste gas stream isscrubbed of entrained methanol before venting to atmosphere.
 9. Thesystem for separating a gas from a process stream of claim 6, whereinthe at least one stripping fluid is a reactant of the chemical process.10. The system for separating a gas from a process stream of claim 1,wherein the stripper unit comprises a gas sparger.
 11. The system forseparating a gas from a process stream of claim 1, wherein the stripperunit comprises a reflux drum.
 12. The system for separating a gas from aprocess stream of claim 11, wherein the stripper unit comprising thereflux drum comprises an integrated stripper/reflux drum which comprisesa stripper section and a reflux drum.
 13. The system for separating agas from a process stream of claim 11, wherein a reflux stream and anon-reflux stream extend and flow downstream from the reflux drum,wherein the separation unit receives the reflux stream.
 14. The systemfor separating a gas from a process stream of claim 1, wherein thestripper unit is associated with the relatively low-pressure column, thesystem further comprising a second stripper unit, wherein the secondstripper unit is associated with the relatively high-pressure column.15. The system for separating a gas from a process stream of claim 1,wherein the second heat exchanger located at the overhead portion of therelatively high-pressure column also serves as a reboiler for a bottomstream of the relatively low-pressure column.
 16. A system forseparating a gas from a process stream, the system comprising: aseparation unit configured to receive the process stream of a chemicalprocess and to separate at least one component of the process stream,the separation unit comprising a first heat exchanger located at anoverhead portion of the separation unit and receiving an overhead streamof the process stream from the overhead portion of the separation unit,the first heat exchanger being configured for condensing at least aportion of the overhead stream of the process stream; a stripper unitconfigured to receive the condensed portion of the overhead stream ofthe process stream from the first heat exchanger, the stripper unitbeing configured for separating the gas from the condensed portion ofthe overhead stream of the process stream by introducing at least onestripping fluid thereunto; and wherein the separation unit is a splitcolumn comprising a relatively high-pressure column and a relativelylow-pressure column, the system further comprising a second heatexchanger, wherein the first heat exchanger is located at an overheadportion of the relatively low-pressure column, and the second heatexchanger is located at an overhead portion of the relativehigh-pressure column to condense an overhead stream of the relativelyhigh-pressure column, wherein the second heat exchanger also serves as areboiler for a bottom stream of the relatively low-pressure column. 17.A method for separating a gas from a process stream, the methodcomprising the steps of: providing a separation unit configured toreceive a process stream of a chemical process and to separate at leastone component of the process stream, wherein the separation unit is asplit column comprising a relatively high-pressure column and arelatively low-pressure column; providing a first heat exchanger at anoverhead portion of the relatively low-pressure column of the separationunit, and a second heat exchanger at an overhead portion of the relativehigh-pressure column, the first heat exchanger being configured forcondensing at least a portion of an overhead stream of the processstream from the relatively low-pressure column; and providing a stripperunit configured to receive the condensed portion of the overhead streamof the process stream from the first heat exchanger, the stripper unitseparating a gas from the condensed portion of the overhead stream byintroducing at least one stripping fluid thereto.
 18. The method forseparating a gas from a process stream of claim 17, wherein the secondheat exchanger located at the overhead portion of the relativelyhigh-pressure column also serves as a reboiler for a bottom stream ofthe relatively low-pressure column.
 19. The method for separating a gasfrom a process stream of claim 17, wherein a second stripper unit isprovided associated with the relatively high-pressure column, the methodfurther comprising providing a condensed portion of an overhead streamof the process stream from the second heat exchanger, the secondstripper unit separating a gas from the condensed portion of theoverhead stream from the second heat exchanger by introducing at leastone stripping fluid thereto.
 20. The method for separating a gas from aprocess stream of claim 17, wherein at least one of the stripper unit orthe second stripper unit comprises a reflux drum integrated with thestripper unit or the second stripper unit.